Solid state optoelectronic device with plated support substrate

ABSTRACT

A vertical solid state lighting (SSL) device is disclosed. In one embodiment, the SSL device includes a light emitting structure formed on a growth substrate. Individual SSL devices can include a embedded contact formed on the light emitting structure and a metal substrate plated at a side at least proximate to the embedded contact. The plated substrate has a sufficient thickness to support the light emitting structure without bowing.

TECHNICAL FIELD

The present technology is directed to solid state lighting (“SSL”)devices constructed on large diameter wafers (e.g., greater than 4inches) and with a plated metal support substrate.

BACKGROUND

SSL devices generally use semiconductor light emitting diodes (“LEDs”),organic light emitting diodes (“OLEDs”), and/or polymer light emittingdiodes (“PLED”) as sources of illumination rather than electricalfilaments, a plasma, or a gas. Mobile phones, laptop computers, digitalcameras, MP3 players, and other portable electronic devices can utilizeSSL devices for background illumination. SSL devices can also be usedfor signage, indoor lighting, outdoor lighting, and other types ofgeneral illumination.

FIG. 1 shows a conventional vertical SSL device 10 including a lightemitting structure 17 having a p-type gallium nitride (GaN) 12,GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 14,and n-type GaN 16 in series. The SSL device 10 also includes a supportsubstrate 18 and a p-type contact 20 between the support substrate 18and the p-type GaN material 12. Conventional support substrates 18 aretypically sapphire or a semiconductor material having a wafer formfactor. The SSL device 10 also includes an n-type contact 22 on top ofthe SSL device 10 that can be wirebonded to an external contact 24 of anexternal host device 26. As voltage is applied between the n-typecontact 22 and the p-type contact 20, electrical current passes throughthe light emitting structure 17 and produces light. The SSL device 10can be made on a wafer that is singulated into individual SSL devices.

Conventional devices use thermo-compression bonding, such ascopper-copper (Cu—Cu) bonding, to attach the light emitting structure 17to the support substrate 18. This process requires high temperatures andpressures that can bow or deform the wafer to the extent that it cracksor warps. Currently LED industry is mostly working with 2-4 inchdiameter substrates, which limits the throughput and increases costsbecause fewer SSL devices can be produced on such small wafers. Even atthese diameters warp and bow of the wafers is a problem for fabricationof LEDs. This problem becomes severe for large diameter (>4 inch)wafers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a vertical SSL device according to theprior art.

FIG. 2 is a side view of a wafer comprising a plurality of SSL devicesaccording to an embodiment of the present technology.

FIG. 3A is a side view of a growth substrate and a light emittingstructure according to an embodiment of the present technology.

FIG. 3B is a side view of a growth substrate, light emitting structure,barrier material, and reflective material according to an embodiment ofthe present technology.

FIG. 4 is a side view of a wafer including a plated substrate accordingto an embodiment of the present technology.

FIG. 5 is a side view of a wafer after the growth substrate has beenremoved from the light emitting structure according to an embodiment ofthe present technology.

FIG. 6 is a side view of a wafer having n-type contacts and singulationlines according to an embodiment of the present technology.

FIG. 7 is a side view of a wafer comprising a plurality of SSL deviceshaving trenches that define mesas according to an embodiment of thepresent technology.

FIG. 8 is a side view of a growth substrate and light emitting structureaccording to an embodiment of the present technology.

FIG. 9 is a side view of a wafer comprising a growth substrate and lightemitting structure including trenches according to an embodiment of thepresent technology.

FIG. 10 is an enlarged view of a trench structure according to anembodiment of the present technology.

FIG. 11 is a side view of a wafer having a plated substrate according toan embodiment of the present technology.

FIG. 12 is a side view of a wafer after the growth substrate has beenremoved according to an embodiment of the present technology.

FIG. 13 is a side view of a wafer having exterior contacts andsingulation lines between individual SSL devices according to anembodiment of the present technology.

FIG. 14 is a side view of a wafer having a patterned resist according toan embodiment of the present technology.

FIG. 15 is a side view of the wafer of FIG. 14 having discrete materialportions formed on the wafer according to an embodiment of the presenttechnology.

FIG. 16 is a side view of the wafer of FIG. 14 wherein the patternedresist has been removed according to embodiments of the presenttechnology.

FIG. 17 is a top view of the wafer of FIG. 14 according to embodimentsof the present technology.

DETAILED DESCRIPTION

Various embodiments of SSL devices, assemblies, and methods ofmanufacturing are described below. As used hereinafter, the term “SSLdevice” generally refers to devices with LEDs, laser diodes, OLEDs,PLEDs, and/or other suitable light emitting structures other thanelectrical filaments, a plasma, or a gas. A person skilled in therelevant art will also understand that the technology may haveadditional embodiments, and that the technology may be practiced withoutseveral of the details of the embodiments described below with referenceto FIGS. 2-13.

FIG. 2 illustrates a wafer 100 comprising several light emitting dies110 formed at the wafer-level according to selected embodiments of thepresent technology. The wafer 100 can be singulated along dividing lines102 to create the individual dies 110. In one embodiment, the wafer 100includes a plated substrate 120, an optional barrier material 130, anoptional reflective material 131, an embedded contact 140, a lightemitting structure 150, and an exterior contact 160 on the lightemitting structure 150. In other embodiments, the embedded contact 140can be highly reflective and/or provide a barrier to prevent diffusionto/from the lighting structure 150 such that the barrier material 130and/or reflective material 131 can be omitted. The plated substrate 120is at the side of the embedded contact 140 and the plated substrate hasa thickness sufficient to inhibit bowing of the light emitting structure150. For example, when the light emitting structure 150 has a diameterof at least 100 mm (e.g., 100 mm, 150 mm, 200 mm, 300 mm, or more), theplated substrate 120 alone without another carrier or support substratecan inhibit bowing at the center of the wafer 100 to less than about 10μm-100 mm, or less than about one of 500 μm, 100 μm, 50 μm, 20 μm, 10 μmor 5 μm (e.g, 0.001% to 1%).

The plated substrate 120 can be electrically and thermally conductive.For example, the plated substrate 120 can be an elemental metal, analloy of different metals, or a plurality of non-alloyed metals. In oneembodiment, the plated substrate 120 includes copper, a copper alloy,nickel, aluminum, and/or other metals. The properties of different metalor alloy materials, e.g. thickness and composition, could be chosen suchthat resulting stress from the deposited materials is substantiallyeliminated and does not result in the wafer warp or bow.

The light emitting structure 150 can be an LED, an OLED, a PLED or othersolid state lighting structure including a first semiconductor material152, a second semiconductor material 154, and an active region 156between the first semiconductor material 152 and the secondsemiconductor material 154. For example, the first semiconductormaterial 152 can be a p-GaN material, the second semiconductor material154 can be an n-GaN material, and the active region 156 can be a quantumwell structure having one or more quantum wells. In several embodiments,the wafer 100 is circular with a diameter of at least four inches, andin many applications the wafer 100 can have a diameter of six inches ormore (e.g. between approximately 150-300 mm). FIGS. 3A-14 illustrateseveral processes, techniques, and methods for producing the dies 110.

FIG. 3A illustrates the wafer 100 at a stage of a process according toan embodiment of the present technology after the lighting structure 150has been formed on a growth substrate 170 apart from the platedsubstrate 120 shown in FIG. 2. In several embodiments, at least part ofthe light emitting structure 150 is grown epitaxially on the growthsubstrate 170. In one embodiment, the growth substrate 170 includessilicon (Si) with a Si(1,1,1) crystal orientation at a surface of thegrowth substrate 170. In other embodiments, the growth substrate 170 canalso include aluminum gallium nitride (AlGaN), GaN, silicon carbide(SiC), sapphire (Al₂O₃), an engineered substrate, a combination of theforegoing materials, and/or other suitable substrate materials.

In selected embodiments, the first and second semiconductor materials152 and 154 include a p-type GaN material and an n-type GaN material,respectively. In another embodiment, the first and second semiconductormaterials 152 and 154 include an n-type GaN material and a p-type GaNmaterial, respectively. In further embodiments, the first and secondsemiconductor materials 152 and 154 can individually include at leastone of gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs),gallium arsenide phosphide (GaAsP), gallium(III) phosphide (GaP), zincselenide (ZnSe), boron nitride (BN), AlGaN, and/or other suitablesemiconductor materials.

The active region 156 can include a single quantum well (“SQW”),multiple quantum wells (“MQWs”), and/or a bulk semiconductor material.As used hereinafter, a “bulk semiconductor material” generally refers toa single grain semiconductor material (e.g., InGaN) with a thicknessgreater than about 10 nanometers and up to about 500 nanometers. Incertain embodiments, the active region 156 can include an InGaN SQW,InGaN/GaN MQWs, and/or an InGaN bulk material. In other embodiments, theactive region 156 can include aluminum gallium indium phosphide(AlGaInP), aluminum gallium indium nitride (AlGaInN), and/or othersuitable materials or configurations. In any of the foregoingembodiments, the first semiconductor material 152, the active region156, the second semiconductor material 154, and any buffer materials(not shown) can be formed on the growth substrate 170 via metal organicchemical vapor deposition (“MOCVD”), molecular beam epitaxy (“MBE”),liquid phase epitaxy (“LPE”), hydride vapor phase epitaxy (“HVPE”),and/or other suitable epitaxial growth techniques.

The orientation of the light emitting structure 150 in FIGS. 3A and 3Bis inverse to what is shown in FIG. 2 because the second semiconductormaterial 154, active region 156 and first semiconductor material 152 aregrown sequentially over the growth substrate 170, and then the embeddedcontact 140 is formed over the first semiconductor material 152. A metalseed material 200 is formed on the embedded contact material 140. Theseed material 200 can be copper or another suitable plating materialthat is deposited onto the embedded contact material using sputtering,vapor deposition, or other techniques so that it is be relatively thin.The plated metal substrate 120 (FIG. 2) can then be formed at the otherside of the light emitting structure 150 proximate the firstsemiconductor material 152.

FIG. 3B illustrates an alternative embodiment according to the presenttechnology. In addition to the materials described above with referenceto FIG. 3A, FIG. 3B includes the barrier material 130 and the reflectivematerial 131. In several embodiments, particularly those in which theseed material 200 comprises copper, the barrier material 130 preventscopper from diffusing into other materials of the stack. The barriermaterial 130 can be tungsten-titanium (WTi), tantalum nitride, or othersuitable materials. The reflective material 131 can be nickel-silver(Ni—Ag), silver (Ag), or other suitable materials. The choice of whetherto include the barrier material 130 and/or the reflective material 131depends on the application for which the dies 110 are designed. Forpurposes of brevity, the remaining figures do not show the barriermaterial 130 or the reflective material 131.

FIG. 4 illustrates a subsequent stage of an embodiment of the presenttechnology, after a relatively large quantity of supporting bulk metalhas been formed monolithically with the seed material. In severalembodiments, the bulk metal can be plated on the seed material to form aplated substrate 210 using electroplating or electroless plating. Theplated substrate 210 can be sufficient to support the light emittingstructure 150 in a manner that inhibits or prevents warping, bowing andcracking. For example, the thickness of the plated substrate 210 can be50-300 μm, such as 150-300 μm, 100-150 μm or 75-150 μm, and the platedsubstrate 210 can have a diameter of at least 4 inches (e.g., 6 inchesor more). The precise thickness of the plated substrate 210 can dependin part upon the material and dimensions of the light emitting structure150 and/or the metal of the plated substrate 210. The material of theplated substrate 210 can also efficiently conduct heat away from thelight emitting structure 150 and can be an electrical contact for thelight emitting structure 150. The plated substrate 210 provides arelatively large contact area that is easy to align with thecorresponding electrical contact on a host structure.

Several embodiments of light emitting dies 110 with the plated substrate210 described above provide several advantages over conventionaldesigns. For example, the plated substrate 210 can prevent bowing of thelight emitting structure 150 that can be caused by lateral interiorstrain between disparate materials of the light emitting structure 150.Such bowing in conventional devices can have many adverse affects, suchas lack of uniformity among wafers, difficulty in mounting thesingulated dies, delamination between layers, and breakage. Conventionalpermanent bond processes such as thermo-compression bonding (e.g.,Cu—Cu) or temporary liquid phase (“TLP”) bonding with inter-metalliccompound formation, nickel-tin (NiSn) bonds, tin-copper (SnCu) bonds andtin-silver (SnAg) bonds, are time-consuming and therefore relativelyexpensive processes. In addition, the thermo-compression bonding processdoes not work as well on irregular surfaces, whereas plated materialscan be readily formed on such surfaces.

FIGS. 3A, 3B, and 4 illustrate the wafer 100 in a first orientation inwhich the growth substrate 170 is shown at the bottom and the platedsubstrate 210 is shown at the top (as represented by arrow A). FIG. 5illustrates a subsequent stage of an embodiment of a method of thepresent technology in which the wafer 100 has been inverted (e.g., arrowA points downward in FIG. 5). The wafer 100 can be mounted to atemporary carrier 240 with a temporary bond. The temporary carrier 240can be an inexpensive recyclable material, such as silicon or tape. Thegrowth substrate 170 is then removed from the light emitting structure150 by grinding, etching, or another suitable technique (shown in dashedlines).

FIG. 6 shows the wafer 100 after the light emitting structure 150 hasbeen exposed by removing the temporary carrier 240 and after formingseveral exterior contacts 250 on the wafer 100. The exterior contacts250 can be formed using conventional metal deposition and patterningtechniques. The wafer 100 can also be exposed to a surface-rougheningoperation. In selected embodiments, each die 110 has one exteriorcontact 250; in other embodiments, each die 110 has a plurality ofexterior contacts 250. The wafer 100 can be annealed at this point, anddifferent configurations can be annealed at different temperatures, suchas at a low temperature (less than about 200° C.) or a high temperature(more than about 200° C.). The temporary carrier 240 can survive therelatively low temperatures, but may not survive temperatures aboveabout 200° C. Accordingly, in the low-temperature embodiments thetemporary carrier 240 remains on the die 110 through the annealingprocesses. In high-temperature processes, however, the temporary carrier240 is removed and the wafer is mounted to a different structure beforesubmitting the wafer to such high temperatures. The dies 110 can besingulated along lines 102 and packaged after forming the exteriorcontacts 250.

The arrangement of the light emitting structure 150 and the exteriorcontacts 250 in FIG. 6 is a vertical LED configuration. In severalembodiments, the plated substrate 210 is electrically conductive, can beused as an extension of the embedded contact 140, and it can provide aheat sink at the base of the die 110. As such, the die 110 can bemounted to an electrically conductive surface having an electrical bias,and the exterior contact 250 can be wirebonded to a lead at the oppositebias to complete the circuit. The plated substrate 210 also effectivelyconducts heat away from the die 110.

FIG. 7 shows another embodiment of the wafer 300 including several dies310 according to the present technology. Many components of thisembodiment are similar to aspects of the embodiments described above.The individual dies 310 of the wafer 300 include a plated substrate 320,an embedded contact 340, a light emitting structure 350, and exteriorcontacts 360. The light emitting structure 350, which can be generallysimilar to the light emitting structure 10 described above withreference to FIG. 1, can include a first semiconductor material, asecond semiconductor material, and an active region. In selectedembodiments, the light emitting structure 350 includes trenches 352separating the light emitting structure 350 into mesas 355. The trenches352 can be aligned with singulation lines between individual dies 310and lined with a dielectric liner 354. The plated substrate 320 can beformed to have projections 322 in the trenches 352, and the dielectricliner 354 can insulate the projections 322 from the light emittingstructure 350. In several embodiments, the projections 322 are integralwith the plated substrate 320.

FIG. 8 illustrates the wafer 300 after the light emitting structure 350and the embedded contact 340 have been formed on a growth substrate 370.Optionally, a barrier and/or reflective material (not shown) can beformed on the growth substrate 370. Aspects of this process are similarto the process described above with reference to FIGS. 3A-6.

FIG. 9 shows an embodiment of a subsequent stage in which the embeddedcontact 340 and the light emitting structure 350 are etched to form thetrenches 352 and the mesas 355. The areas above the mesas 355 can becovered with a mask, and the wafer 300 can be etched, for example via awet etch, through the exposed portions of the embedded contact materialand the light emitting structure 350 to form V-shaped trenches 352. Inselected embodiments, the trench 352 can be etched, then dielectricliners 354 can be deposited and patterned. Then the embedded contacts340 can be deposited and patterned. In several embodiments, the trenches352 extend completely through the light emitting structure 350 and intothe growth substrate 370. In other embodiments, the V-shaped trenches352 do not reach completely through the light emitting structure 350,leaving a small connecting portion of the light emitting structure 350at the base of the trench 352. In embodiments in which the individualdies 310 (see FIG. 7) are to be singulated, the singulation procedurecan cut through this small connecting portion. The dimensions of themesas 355 correspond to the final size of the light emitting dies thatwill be ultimately produced from the wafer 300. The tolerance betweenthe dimensions of the mesas 355 and the final intended size of the lightemitting dies can be somewhat large because the wafer 300 is singulatedalong the trenches. The etching processes described herein can also beperformed using dry etch processes.

FIG. 10 is an enlarged view of a single trench 352 according to anembodiment of the present technology. During a wet etch process, thecrystal structure of the light emitting structure 350 is preferentiallyetched at an angle to form angled walls 350 a. When the trenches 352 areto be filled with a conductive material, such as a plated metal, thedielectric liners 354 are formed before the trenches 352 are filled. Thedielectric liners 354 can be formed by depositing a thin conformalmaterial of dielectric material over all of the exposed surfaces. Inselected embodiments, the dielectric material on top of the mesas 355(shown in dashed lines) can be removed using a mechanical,chemical-mechanical or etching process. In other embodiments, thedielectric material can be deposited after the trenches 352 are etchedbut before the mask is removed from the wafer 300 such that a portion ofthe thin dielectric liner 354 remains in the trenches 352 after removingthe mask.

FIG. 11 illustrates yet another stage of the process for manufacturingthe wafer 300 according to an embodiment of the present technology.After forming the trenches 352 and the dielectric liners 354, thematerial for the embedded contacts 340 can be deposited and the platedsubstrate 320 can be plated over the light emitting structure 350 and inthe trenches 352. In selected embodiments, the contacts 340 can beformed on top of the mesas 355 and not in the trenches 352, as shown inFIG. 11. Alternatively, the contacts 340 can be formed on the mesas 355and in the trenches 352, as shown in FIG. 7. As described above, inseveral embodiments a seed material (not shown) can first be depositedover the wafer 300 to facilitate the plating process. The platedsubstrate 320 can be metal, be thick enough to support the wafer 300,and prevent or at least inhibit bowing. For example, the thickness ofthe plated substrate 320 can be 50-300 μm, such as 150-300 μm, 100-150μm or 75-150 μm. This process eliminates the need for thermo-compressionor inter-metallic compound bonding, and it allows the wafer 300 to havea larger diameter. In several embodiments, the wafer 300 can be at leastfour inches in diameter, and in many cases 6-8 inches in diameterwithout undo bowing.

The wafer 300 is oriented with the plated substrate 320 facing the topof FIG. 11, as shown by arrow A. FIG. 12 illustrates another stage ofthe method after a temporary carrier 380 has been attached to the platedsubstrate 320, the growth substrate 370 has been removed, and the waferhas been inverted (e.g., see Arrow A). FIG. 13 shows yet another portionof the method according to embodiments of the present technology afterexterior contacts 390 have been formed on individual dies 310. Asdiscussed above, the dies 310 can be annealed at a high or lowtemperature. If the annealing process is performed at a high temperaturethat would harm the bond line between the temporary carrier 380 and thesubstrate 320, the temporary carrier 380 can be removed prior to formingthe exterior contacts 390. Otherwise, the temporary carrier 380 canremain in place as the exterior contacts 390 are formed.

FIGS. 14-17 illustrate yet another embodiment of the present technologyin which a patterned plating is formed on a substrate at an intermediatestage of production of light emitting dies. FIG. 3A and the associateddescription above relate to an intermediate step in which a seed layer200 has been formed on an embedded contact 140. In place of (or inaddition to) forming the plated substrate 210 on the seed layer, thefollowing structures and processes can be used. FIG. 14 shows a wafer400 comprising a growth substrate 470, a light emitting structure 450,an optional barrier material 430, and a metal seed layer 420, similar toembodiments described above with reference to FIGS. 1-6. The wafer 400also includes a patterned resist 440 formed at intervals approximatelyequal to the size and configuration of the individual dies that willeventually be formed by these processes and singulated into individualSSL devices. In selected embodiments, the patterned resist 440 can alignwith the planned singulation paths between the dies. In otherembodiments, however, the patterned resist 440 can be alignedindependently from the singulation paths.

FIG. 15 illustrates a further stage in the process according toembodiments of the present technology in which discrete plated materialportions 442 are plated using any suitable plating or metal depositiontechnique. In selected embodiments, the individual discrete materialportions 442 are prevented from coalescing with adjacent materialportions 442 by the width of the patterned resist 440. In selectedembodiments the width of the patterned resist 440 on the wafer 400 is atleast approximately twice the thickness of the discrete plated materialportions 442. FIG. 16 illustrates a further portion of the process inwhich the patterned resist 440 is removed, leaving the discrete materialportions 442 on the wafer 400 and bonded with the seed material. Theresulting structure is a series of discrete plated material portions 442with streets 444 running between them where the patterned resist 440once was.

FIG. 17 is a top view of the discrete material portions 442 and thestreets 444 running between them. The streets 444 can be orthogonal asshown, or they can have another suitable orientation. The streets 444relieve stresses in the wafer 400, and therefore mitigates bowing anddeflection of the wafer 400. Using these techniques, the wafer 400 canbe a much larger size of six or eight inches or more than withconventional techniques which are generally limited to two or fourinches.

The processes described herein are generally applicable to an entirewafer and all of the SSL devices on the wafer. It is to be understood,however, that in several embodiments, one or more of the processes canbe localized to a predetermined group of SSL devices, and that not allof the processes need be uniformly applied to the entire wafer.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thetechnology. In addition, many of the elements of one embodiment may becombined with other embodiments in addition to or in lieu of theelements of the other embodiments. Accordingly, the technology is notlimited except as by the appended claims.

We claim:
 1. A method of manufacturing solid state lighting devices,comprising: forming a light emitting structure on a circular growthsubstrate, wherein the growth substrate and the light emitting structureare at least six inches in diameter, wherein the light emittingstructure has a first face facing the growth substrate and a second facefacing away from the growth substrate; forming an embedded contacthaving a first side in physical contact and electrically coupled to thesecond face of the light emitting structure, the embedded contact havinga second side opposite the first side; etching a plurality of v-shapedtrenches through the embedded contact and into the light emittingstructure, wherein the trenches separate the light emitting structureinto individual mesas; lining entire surface of each of the plurality ofthe individual trenches with a dielectric liner, wherein the dielectricliner ends at the second side of the embedded contact; forming a platedsubstrate on the individual mesas at the second side of the embeddedcontact and filling the trenches, wherein a first side of the platedsubstrate faces toward the mesas and a second side opposite the firstside faces away from the mesas; attaching a carrier to the second sideof the plated substrate; removing the growth substrate from the lightemitting structure; and forming exterior contacts at the first face ofthe light emitting structure.
 2. The method of claim 1, furthercomprising: forming a barrier on the embedded contact, wherein etchingthe plurality of v-shaped trenches comprises forming V-shaped trenchesthrough the light emitting structure, the embedded contact, and thebarrier.
 3. The method of claim 1 wherein etching the plurality oftrenches comprises etching through the light emitting structure toexpose a portion of the growth substrate.
 4. The method of claim 1wherein etching the plurality of trenches in the light emittingstructure comprises using a wet etch that penetrates to the growthsubstrate.